Some composite synthetic strings are already known. Described in FR-A-2 491 098 is a synthetic string with two components: polyamide multifilament threads and polyurethane, the multifilaments being integrated in a matrix of polyurethane. The polyurethane binder, whose elastic behavior is quite superior to that of polyamide, makes it possible to obtain, with a particular structure of the string, a high breaking strength and an average hardness expressed by rapid return of the string to its initial position after impact of a ball.